My favorite Buster Keaton flick, and this one has got a great score by The Club Foot Orchestra.
In an age before computer generated effects Sherlock Jr's out of control ride on the handlebars of a motorcycle is astonishing. It is a sequence that could never be duplicated in the modern era. Buster plays a theater projectionist with dreams of becoming a master sleuth. When he loses his girl to "The Local Sheik" Buster retreats to a dream world where he literally steps into the movie he is screening and becomes the "world's greatest detective".